Don Quixote, Sadler's Wells London

It has a crumbling old-world grandeur. It has an ancient and autocratic leader who retains an iron grip. It has suffered from cultural isolation and a dire lack of cash, yet its sunny charm is lauded around the world. What is true of the island country of Cuba is also true of the Ballet Nacional de Cuba, making a return visit to London after a triumph last summer, its first showing in Britain for 20 years. This time, though, the cracks are showing, and in Don Quixote it was only an 11th-hour burst of fireworks that saved the whole affair.

The fault lies largely with the production, staged, like all the company's classical work, by its formidable founder Alicia Alonso. Now 84 and blind, she is as firmly in control as she was half a century ago, when as one of the world's greatest ballerinas (making her name with American Ballet Theatre) she introduced her art form to her home country with such success that almost every athletic Cuban child now tries for state-funded education in ballet. This explains how a country with a population of just 11 million can produce a ballet company to compete on the world stage.

We're told that Alonso's production of Don Quixote dates from 1988, but it has the feel, and dowdy look, of Russia's Soviet era, with ugly sets, ill-fitting costumes and a preponderance of white tights for the men that leave little to the imagination (except in the case of one hapless dancer who appeared to have forgotten his box, thus creating a considerable distraction as one wondered which way - as it were - he was going to land after each jump). The odd sartorial nod to authenticity - as in the village men's long black hairnets - succeeded only in looking odd. And the dryads of the vision scene wear frocks of such a violent hue that by rights the dreaming Don should be wide awake and screaming.

Technical prowess would make this matter less, but the truth is that some of the dancing in this Don Quixote lacks ease and grace, particularly in the early scenes, which in Alonso's version are short on memorable steps, even in the effusive group dances. And wasn't it wayward and cruel to ask the matadors to negotiate huge synchronised sideways leaps while securing their cape with one arm, just as if it was stuck in a sling? Elsewhere the men's exaggerated high-chested posture made them resemble puffed-up pigeons desperate to mate.

To see how it should be done, you looked to the evening's leads, Viengsay Valdes and Joel Carreno. Though very little spark crackles between them, individually each is superb, despite choreography that gives them scant chance to strut their stuff until late in the ballet. Though Alonso's version sticks pretty close to what's known of the 19th-century choreography, it mucks around with the running order, saving too many of the best bits till last.

The wait, however, is worth it, and midway through the third act the show suddenly opens the throttle. Of course the final pas de deux is always a crowd-pleaser, showing off many of ballet's favourite stunts, from extravagant double-splits jumps to strings of double and triple fouettes that have the audience counting them off on their fingers. Before the 20th-century only two or three ballerinas in the world could do this. Now every company has its whip-turn queen, but never have I experienced such a full-on blast of dazzling extra effects. "Now watch this," said Valdes's smile as, having knocked off the standard 32 fouettes as swiftly and cleanly as the swing-needle on a Singer, she closed with a melting rallentando and a series of slow embroidery stitches. Still balancing on one toe and refusing the support of her partner, she oh-so-teasingly folded and unfurled her raised leg in a smooth passage from arabesque to attitude, fore and aft, like a cat swinging a mouse by its tail. Hearts stopped beating. Polite gasps turned to groans of incredulity. Yet there was more. The couple's final allegro saw Carreno flip Valdes high into the air, break her fall on the nape of his neck and swing her into a fish dive. This was more than a circus act. It had the 22-carat gleam of artistry. Catch a last glimpse of these extraordinary performers in their gala programme today.